Cracking process



June 4, 1946. H. H. MEIER CRACKING PROCESS Filed April 1o, 1944 cons m2E Sainz osseo oo Piuma June 4, 194s UNITED STATES PATENT ori-lcsCRACKING PROCESS ration of Delaware Application April 10, 1944, SerialNo. 530,366 Claims. (Cl. 1949) The present invention is directed to thethermal treatment of hydrocarbon oils, and more particularly to thecracking of hydrocarbon oils to produce valuablev products.

In accordance with the present invention, hydrocarbon oils, such as gasoil obtained from petroleum, are subjected to treatment includingpleted, the nely divided catalyst is separated gn from the oil,regenerated and subsequently returned to the catalytic cracking zone.The conditions maintained in the catalytic reaction system may be variedin accordance to the charge stocks being treated, but in general thetemperatures will be in the range of 850 to 1000 F., with pressuresranging from to 20 pounds per square inch. It is usual to employ analumina silica catalyst in commercial catalytic cracking units, butother catalysts well known to the catalytic cracking art may be employedif desired. The thermal cracking step employed in the present inventionmay be carried out by subjecting the oil being reacted to a temperaturein the range of 1000 to 1300" F. under a pressure ranging from 35 50 to800 pounds per square inch. If desired, steam may be injected into thematerial being thermally cracked in amounts up to 100 mole per cent..

based on the charge.

The period the oil is retained under thermal cracking conditions may bevaried over a wide range, with contact times varying from an order of .5to 5 seconds up to more than 300 seconds.

In its more speciilc aspects the present invention may be described asinvolving the catalytic cracking of gas oil, the separation of afraction in the naphtha boiling range from the product of the catalyticcracking process, the thermal cracking of this fraction, and thesubsequent nishing of the thermally cracked fraction to obtain anaviation grade naphtha. When employing this process the product from thecatalytic cracking step may-.be fractionated to obtain substantialamounts ofbutylenes and isobutanes therefrom,

2 as well as the naphtha fraction which is subsequently subjected tothermal cracking. I

It is an advantage of the present invention that the throughput of theunit wherein the catalytic cracking step takes place may-besubstantially increased above its normal rating which results inincreased amounts of aviation grade naphtha and butylenes and isobutanesfor a given capacity of a. catalytic cracking unit. An additionaladvantage ofthe present invention is that a large amout of stableaviation grade naphtha may be producedawith a minimum loss of componentscharged to the process. Other objects and advantages of the presentinvention may be seen from the following description taken with thedrawing, mwhich the" sole ligure is in the form' of a now sheetdiagrammatically illustrating a preferred method for conducting thetreatment of the present invention.

Turning now to the drawing,a charging stock, such as gas oil, is passedvia inlet II into catalytic cracking unit I2. Within the cracking unitthe gas oil is subjected to suitable thermal conditions in the presenceof a catalyst to produce substantial amounts of hydrocarbons in thenaphtha boiling range. as well as lighter hydrocarbons, such asbutylenes and isobutane. The temperature conditions maintained withincracking unit I2 may be within the range of 800 3o to 1000 F., inaccordance with conventional practice of operating duid catalystcracking units, and the other conditions within the unit may also bemaintained in accordance with conventional practice. The product fromunit I2 may` be withdrawn via line I3 and discharged into iractionatingcolumn I4. Within fractionating unit I4 the product from the catalyticcracking unit may be divided into a plurality of fractions..

' A heating coil I5 is provided in the lower end of fraction withdrawnas a side stream may advanthe unit to aid in the vaporization of thehydrocai-bons therein, and the feed into this unit may be divided into aheavy bottoms and Withdrawn via outlet I6, and a light fractionconsisting principally of butylenes, isobutanes and light naphtha whichmay be Withdrawn as overhead from the top. of the tower via line Il. Inaddition, a selected fraction in the naphtha boiling range may bewithdrawn as a side stream from outlet- I8 and passed-to thermalcracking unit I9. The naphtha tageously have a boiling range o f from200 to 400 F. AColumn 'I4 and the streams drawn therefrom are showndiagrammatically in thefigure, f and it is to be understood that thedistillation stepmay beconducted in a plurality of-columns,

and that the naphtha fraction withdrawn for subsequent treatment in thethermal cracking unit may be divided into a number of fractions and eachfraction treated by thermal cracking. For example, a naphtha'fractionboiling in the range of 200 to 350 F. and another naphtha fractionboiling in the range of 350 to 400 F. may be separately withdrawn fromthe distillation unit and separately subjected to thermal cracking.

In thermal cracking unit I9 the naphtha fraction may be subjected to atemperature in the range of from 1000 to 1300o F., depending upon thecharacter of the fractions being treated, with pressures ranging from 50to 800 pounds per square inch. If desired, steam may be injected withthe naphtha fraction being cracked in accordance with the well knowntechnique of thermal cracking fractions in the naphtha boiling range.The product from thermal cracking unit I9 is discharged via line 20 intofractionating column 2l, provided with heating coil 22.

The material in column 2i may be divided into a heavy fraction Withdrawnas bottoms vla outlet 23. a medium fraction withdrawn as a side streamvia outlet 24, and a light fraction withdrawn as overhead via line 25.It will usually be found desirable to operate distillation tower 2l toseparate a side stream having a boiling range approximately that treatedin therma1 cracking unit I9. If, for example, the naphtha fractioncharged to thermal cracking unit I9 had a boiling range of 200 to 400 FJit is desirable to Withdraw a fraction of this same boiling range as aside stream via line 24. This side stream fraction is high in aromaticcontent and is advantageously finished to obtain an aviation gradenaphtha. In order to carry out this finishing step, sulfuric acid may beinjected into the fraction iiowing through line 24 by means of line i0,

'the two components being admixed in mixer 26 and subsequentlydischarging through line 26 into settling vessel 21. Acid sludge iswithdrawn from the lower portion of vesse1 21 by means of outlet 28, andthe naphtha fraction is withdrawn from an upper portion of vessel 21 bymeans of line 29, has added thereto sodium hydroxide by of 200 to 350 F.as overhead, vialine 38, with the remainder withdrawn as bottoms by line39. The overhead fraction is preferably caustic washed with sodiumhydroxide added thereto through inlet 40. the admixture passed tosettler 4I where it is allowed to settle into a spent caustic layer andnaphtha layer, and the spent caustic layer withdrawn through outlet 48.The naphtha fraction may be withdrawn from settler 4| by means of line42, and is ready to be used as an aviation naphtha either with orwithout further blending. It is commercially desirable to blend thisstock with various components, and, as shown in the drawing, aninhibitor may be added to the fraction flowing through line 42 by meansof inlet 43, an isopentane fraction may be added via line 44, analkylate fraction via line 45, and an anti knock agent, such astetraethyl lead, via line 46. The naphtha fraction with these variousaddition agents may be discharged into storage 41, and will be afinished high quality aviation grade fuel.

An indication of the high quality of products by the practice of thepresent invention, as well as the yield, is found in the followingtable. In obtaining the data set forth therein, 30 A. P. I. gas oilfractions were first subjected to cracking in a fluid catalyst crackingunit at a maximum reactor temperature of 975. F. The product from theuid catalyst cracking unit was then distilled to separate fractions inthe naphtha boiling range and the naphtha fractions then subjected tocracking in the therma1 cracking unit at a temperature ranging between1000 F. and 1030 F. and at a pressure of 750 pounds per square inch. Theadvantage of subjecting the fractions to the recracking in the thermalunit is indicated by the substantial increase in octane number obtainedby passing the fraction through the thermal cracking unit. In the table,F. C. C. U. is an abbreviation for fluid catalytic cracking unit, and T.C. U, is an abbreviation for therma1 cracking unit. It will be seen thatthe rst five runs were carried out using a parai'linic gas oil as thecharging stock and runs VI and VII were carried out with a naphthenicgas oil as the charging stock.

Table I l Perainlc'gas oil Natnic Charge to F. C. C. U.

Run Run Run Run Run Run Run I II III IV V VI VII l Conversion at F. C.C. U percent-. 67 67 60 60 60 63. 6 63.6 Tem rature of T. C. U 1,010 1,010 1, 000 1,015 1.030 1, 010 1,010 Yiel from T. C. U. percent feed 63.0 16. 4 61.5 6l. 7 55. 2 77. 2 19.2 Fraction to T. C. U 205-350 205-350205-350 205-350 205-350 350-400 Octane No.:

Before recracklng- 1-C A.S.T.M.) 86.2 91.0 91.6 91 6 92.2 3-0 AN) I. M.E. P'. 121 192.8 192.8 192 8 129 Octane No.:

After recrecklng- 1C A.S.T.M.) 93.2 90. 7 95.8 97.4 98. 7 99. 2 96. 73-C AN) I. M. E. P 131 153 215 @6.6 241 181 138 means of4 inlet line 30,and the two components are then admixed by passing through mixer 3| anddischarge into settling vessel 32. Spent sodium hydroxide solution iswithdrawn from a lower portion of vessel 32 by means of outlet line 33.A naphtha fraction is withdrawn through line 34 and has alkali solutionor soap bottoms added thereto by inlet line 35 and is discharged intofractionating tower 36, provided with heating coil 31. It is preferredto operate distillation It will be noted that runs III, IV and V wereprocessed in the same manner in the :duid catalytic cracking unit, butwere thermally treated at temperatures of 1000, 1015 and 1030 F.,respectively, in the thermal cracking unit. It will be observed that theuse of the higher temperatures in the therma1 catalytic cracking unitproduced a higher octane number in the nished product, but lowered theyield.

Because oi' its large initial investment, it is tower 36 to'remove afraction boilingintbe range 75 usually desirable to employ the iluidcatalytic cracking unit to the utmost advantage., It is quite oftenconvenient to determine the value of the output of the uid catalyticcracking unit by determining the amount grade naphtha and butylenes andisobutanes which may be obtained from its operation. In order toascertain the optimum rate of operation of the fluid catalytic crackingunit described above. comparative runs were made using different ratesof feed. The results of these runs are shown in the followings table.The uid catalytic cracking unit employed had a rated'capacity of 13,300barrels per day at 65% conversion on 30 A. P. I. gas oil. Whenconducting a series of comparative runs it was found that by loweringthe input the per cent conversion obtained was increased, but that byincreasing the throughput the amount of converted product measured inbarrels per day was increased. The exemplification of these results isset out in the following table, in which run I shows the quality andamount of product obtained from the uid catalytic cracking unit whenoperating at a throughput of 10,000 barrels per day, while run IIindicates the results obtained with a throughput of 17,600 barrels per`day. The product from the fluid catalytic cracking unit was distilledanda naphtha fraction boiling in the range of 205 to 300 F. was thensubjected to a thermal cracking operation carried out at l5 F. Thesubstantial per day of aviationl in Table I and Table II, it will beevident that naphthas obtained from the uid catalytic cracking unitwhich were of marginal grade for aviation fuel have been converted intohigh quality aviation naphthas. the catalytically cracked fractions notonly produces high grade aviation naphthas, but in addition allows thecatalytic cracking unit to be operated with a very high throughput, withan inthe rating of the naphthas subjected to the ther- Y mal crackingstep is substantially improved, the

creased product on a barrels-per-day basis, both of naphtha fractionsand also butylene and isobutane fractions. It is to be noted thatalthough amount of material lost by this treatment is rela-` tivelysmall.

While I have disclosed specic examples illustrating the practice of thepresent invention, the

conditions set forth in these examples are given improvement of theproduct obtained when thermally cracking the naphtha separated from theproduct of the uid catalytic cracking unit is evident in the octanenumbers of the fractions by way of illustration only and are notintended as limitations.l It will be appreciated that the. temperatureof operation in the fluid catalytic cracking unit, the charging rate,catalyst used and the temperature of operation in the thermal crackingunit and the charging rate, as well as the steps of finishing thenaphtha. fraction withdrawn from the thermal cracking unit may be variedsubstantially Without departing from the scope of the present invention,and it ismy intention to embrace such changes by the hereto appendedclaims.

I claim: V

1. A method for treating hydrocarbons comprising the steps of charging apetroleum fraction shown. in the gas oil boiling range to a catalyticcrack- Table II mii-350 F. fraction from F. C. C. U. 205-850 F. fractionfrom T. O. U.

Run Ce t?? (iPnerio't Octane No. Octane No.

B/D percent Amt. Amt.

B/D 1-o a-o (m2) B/D 1-o a-o (AN) (A. s. T. M.) I. M. E. (s. s. T. M.)I. M. E. P.

I 10,000 71 1,251 00.0` 21s 1,005 91.0 200 n 17,000 6o 2,153 sas ist1,015 95.1 21e Although not shown inthe table above, the yield ofbutylenes and isobutanes on a barrelsper-day basis is also increased byincreasing the charge rate of the fluid catalytic cracking unit. 'I'heyield of butylenes formed in the fluid catalytic cracking -unitdecreases from 9.2% to 7.0% as the feed rate is increased from 10,000 to17,600 barrels per day, but the amount of butylenes obtained increasesfrom 920 barrels to 1.225 barrels per day over the same range.Similarly, the yield of isobutane is decreased froml9.3% to 6.3%, butthe amount produced increases from 930 barrels to 1,115 barrels pei` dayas the feed rate is changed from 10,000 to 17,600 barrels per day.

It is postulated that the combination treatment including a preliminaryfluid catalytic cracking step followed by a thermal crackingstep-produces an improved quality product by the forming of largeamounts of aromatics in the catalytic cracking step and thedecomposition of naphthenic compounds into aromatics in the thermalcracking step. It has been found that the naph-- ing unit andmaintaining it therein at a tempounds of acid perature in the range of850 to 1000 F. to 'cause substantial cracking thereof, removing theprodnot resulting from the cracking of the fraction in the gas oilboiling range from the catalytic cracking unit, separating a fraction inthe naphtha boiling range therefrom, passing said fractionto a thermalcracking zone maintained in the temperature range of 1000 to 1300 F. tocause cracking thereof, removing product resulting from the cracking ofthe fraction in the naphtha. `boiling range from the thermal crackingzone and subjecting said product to distillation conditions in afractionating zone to separate a naphtha fraction boiling above 200 F.and no higher than 400 F.

2. A method in accordance with claim 1 in which the naphtha separated inthe fractionating zone is treated with sulfuric acid to form a finishedaviation grade naphtha.

3. A method for treating hydrocarbons com prislng the steps ofsubjecting a petroleumv fraction in the gas oil boiling range tocracking conditions ln a catalytic cracking zone at a temperature ofapproximately 950 F., removing the product; resulting from the crackingof the fraction in the gas oil boiling range from the catalytic crackingzone and fractionating in a first The thermal treatment oivfractionating zone to separate a side streaxn boiling above 200 F. andno higher than 400 F., subjecting said fraction to cracking conditionsin a thermal cracking zone maintained in a temperature range of 1000" to1300 F., removing product resulting from the ,cracking of the sidestream fraction from the thermal cracking zone to a second fractionatingzone, separating a naphtha fraction from the second separating zoneboiling above 200 and no higher than 400,F. and subjecting said naphthafraction to finishing treatments to obtain an aviation grade motor fuel.

4. A process in accordance with claim 3 in which the charging rate ofgas oil to the catalytic cracking zone is adjusted of approximately 60%.

5. A process in accordance with claim 3 in which butylenes andisobutanes are separated from the product from the catalytic crackingzone in the first fractionating step, and in which the gas oil ischarged to the catalytic cracking lmit at a suciently high rate toobtain a conversion therein of approximately 60%.

HERBERT H. MEIER.

to obtain a conversion

